260 THE CANADIAN ENTOMOLOGIST. 



to the brood, and many of the youngest larv?e died in their cells, in a few 

 weeks my vespiary came to an end, having been under observation from 

 the 23rd of June to about the middle of July. From the study made of 

 its habits during that time I am able to give the following review of the 

 life history of Xenos. Many of the facts are not new, but have been so 

 rarely observed that it will not be amiss to repeat them. 



The young issue from a slit in the so-called head, which may after all 

 be the anal extremity of the mother, after it has protruded from the body 

 of the wasp. A single female gives birth to hundreds if not thousands of 

 them. They are at birth six-legged triungulins, fairly active, but so small 

 that they are barely visible to the naked eye. Under a hand-lens they 

 bear a marked resemblance to the young of scale insects, having a similar 

 oval form and a pair of long anal stylets. They wander over the body of 

 the wasp, apparently giving it no inconvenience, and are also seen crawl- 

 ing about the nest. In some way they pass into the bodies of their hosts 

 while the latter are very young larvje. Within the bodies of the wasp- 

 grubs they occupy varying positions, but always in the fatty matter near 

 the skin. Their form now becomes very elongate and worm-like, without 

 any organs visible under low magnifying powers. Their delicate and 

 transparent bodies seem to be simple sacks filled with fatty matter, in 

 which float globules of oil. When full grown the larva of Xenos is about 

 three-eighths of an inch long. The female parasite finally acquires a 

 chitinous plate at one end of the body and becomes adult. The male 

 shortens to about one-half its former length, thickens and becomes cylin- 

 drical, the anterior end is chitinous and shows traces of faceted eyes and 

 rudiments of other organs, the convex end of this chitinous portion is 

 separated by a sutural line, and forms the mask-like cap of the puparium. 

 While the wasp is in pupa, or at least before it has left its cell in the 

 comb, the parasites of both sexes push their chitinous extremity out of 

 its body, appearing at the sutures of the last four or five segments. 

 Within a few days after the wasp has left its pupa cell, the male Xenos 

 pushes off the lid or cap of its puparium and makes its appearance, tak- 

 ing flight at once. It never alights or rests in its flight from the moment 

 of birth until it falls exhausted and dying, worn out by the incredible 

 activity of its short existence. Its life as an active imago cannot be 

 longer than fifteen or twenty minutes, if as long, and during this time it 

 exhibits fiery energy, and flies so rapidly that the eye can hardly follow it. 

 Its legs are shrunken and entirely useless organs, and I think the muscles 



